1
$\begingroup$

This is for a DIY project I'm working on. I know I could just monitor the charging process and unplug before the capacitor blows, or get a more suitable power supply, but it just so happens that I have a bunch of capacitors rated at 1000 V and a transformer that gives me 6000 V DC. I'd like to use this rather than spend extra on getting another transformer.

Let's say I put the capacitor in parallel with a resistor, and this in series with another resistor, i.e. I'm using a potential divider to limit the capacitor output, like this:

enter image description here

Initially, the capacitor is going to be like a short circuit, so it'll charger very rapidly, but as it fills up, more charge will go through R1 instead. When the capacitor is charged at $V = V_{in} \times R_1 / (R_1+R_2)$, there should be no current passing through the capacitor.

This seems like a very simple situation to me, but for some reason I don't see anyone doing this or any information about a circuit like this online (or maybe I'm just not using the right search terms...)

Am I missing out something fatal that'll completely screw up my capacitors if I try this?

Also, any tips on choice of resistor size? I'd probably want to use the most resistant resistors I have to keep current flow small.

$\endgroup$
0
$\begingroup$

So to get 1000V from the 6000V supply you need a ratio of 1:5

higher resistance will cause slower charging.

Pick a resistance that would give an acceptable result if used with a 1000V supply, then choose your R1,R2 such that their parallel combination is that resistance. and their ratio is 1:5.

can you instead use a step-down tranformer on the input to the 6000V supply?

$\endgroup$
  • $\begingroup$ Just to clarify, when you say "pick a resistance that would give an acceptable result if used with a 1000 V supply", you mean adding a resistance in series with the capacitor to slow down the current to the capacitor, right? As for the step down transformer, I don't have one at the moment, just avoiding having to spend on additional stuff for a one-time-off project. $\endgroup$ – Nic Jan 8 '17 at 8:08
  • $\begingroup$ yes, I mean in series with the 1000V supply, between it and the capacitor. The transformer would only need to be about 1/36 the size of the one in the 6000V supply $\endgroup$ – Jasen Jan 8 '17 at 8:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.